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<FONT color="green">001</FONT>    package project3.three;<a name="line.1"></a>
<FONT color="green">002</FONT>    <a name="line.2"></a>
<FONT color="green">003</FONT>    import project3.lex.Lex;<a name="line.3"></a>
<FONT color="green">004</FONT>    import project3.lex.Token;<a name="line.4"></a>
<FONT color="green">005</FONT>    import project3.lex.TokenType;<a name="line.5"></a>
<FONT color="green">006</FONT>    <a name="line.6"></a>
<FONT color="green">007</FONT>    /**<a name="line.7"></a>
<FONT color="green">008</FONT>     * The parser builds a parse tree of nodes.  The tree is actually built from<a name="line.8"></a>
<FONT color="green">009</FONT>     * special types of nodes.  The special types of nodes are: &lt;b&gt;List&lt;/b&gt;,<a name="line.9"></a>
<FONT color="green">010</FONT>     * &lt;b&gt;DatalogProgram&lt;/b&gt;, &lt;b&gt;Rule&lt;/b&gt;, and &lt;b&gt;Token&lt;/b&gt;.  The other nodes in<a name="line.10"></a>
<FONT color="green">011</FONT>     * the program are specializations of &lt;b&gt;List&lt;/b&gt;.  This class has no<a name="line.11"></a>
<FONT color="green">012</FONT>     * attributes.  It has the method "checkFor" which is used by most of its<a name="line.12"></a>
<FONT color="green">013</FONT>     * children.<a name="line.13"></a>
<FONT color="green">014</FONT>     *<a name="line.14"></a>
<FONT color="green">015</FONT>     * &lt;pre&gt;<a name="line.15"></a>
<FONT color="green">016</FONT>     * Domain Implementation:<a name="line.16"></a>
<FONT color="green">017</FONT>     *     -- none<a name="line.17"></a>
<FONT color="green">018</FONT>     * &lt;/pre&gt;<a name="line.18"></a>
<FONT color="green">019</FONT>     *<a name="line.19"></a>
<FONT color="green">020</FONT>     * Last Modified: 21 Feb 2006<a name="line.20"></a>
<FONT color="green">021</FONT>     *<a name="line.21"></a>
<FONT color="green">022</FONT>     * @author Scott N. Woodfield<a name="line.22"></a>
<FONT color="green">023</FONT>     * @version 1.0<a name="line.23"></a>
<FONT color="green">024</FONT>     * @see<a name="line.24"></a>
<FONT color="green">025</FONT>     *   &lt;a href=<a name="line.25"></a>
<FONT color="green">026</FONT>     *      "../../srchtml/project3/Node.html"<a name="line.26"></a>
<FONT color="green">027</FONT>     *      &gt;Source Code<a name="line.27"></a>
<FONT color="green">028</FONT>     *   &lt;/a&gt;<a name="line.28"></a>
<FONT color="green">029</FONT>     */<a name="line.29"></a>
<FONT color="green">030</FONT>    abstract public class Node<a name="line.30"></a>
<FONT color="green">031</FONT>    {<a name="line.31"></a>
<FONT color="green">032</FONT>        /**<a name="line.32"></a>
<FONT color="green">033</FONT>         * checkFor determines if lex.front() has the expected TokenType. If so<a name="line.33"></a>
<FONT color="green">034</FONT>         * returns the next token and pops lex.  If not, it throws an exception.<a name="line.34"></a>
<FONT color="green">035</FONT>         * This is a method used in almost all classes and is written at this<a name="line.35"></a>
<FONT color="green">036</FONT>         * level so we only have to write it once.<a name="line.36"></a>
<FONT color="green">037</FONT>         *<a name="line.37"></a>
<FONT color="green">038</FONT>         * &lt;p&gt;<a name="line.38"></a>
<FONT color="green">039</FONT>         * &lt;table&gt;<a name="line.39"></a>
<FONT color="green">040</FONT>         *   &lt;tr&gt;<a name="line.40"></a>
<FONT color="green">041</FONT>         *     &lt;td valign=top&gt;<a name="line.41"></a>
<FONT color="green">042</FONT>         *       &lt;b&gt;Precondition&lt;/b&gt;:<a name="line.42"></a>
<FONT color="green">043</FONT>         *     &lt;/td&gt;<a name="line.43"></a>
<FONT color="green">044</FONT>         *     &lt;td valign=top&gt;<a name="line.44"></a>
<FONT color="green">045</FONT>         *       lex &amp;ne; null<a name="line.45"></a>
<FONT color="green">046</FONT>         *     &lt;/td&gt;<a name="line.46"></a>
<FONT color="green">047</FONT>         *     &lt;td valign=top&gt;<a name="line.47"></a>
<FONT color="green">048</FONT>         *       AND<a name="line.48"></a>
<FONT color="green">049</FONT>         *     &lt;/td&gt;<a name="line.49"></a>
<FONT color="green">050</FONT>         *   &lt;tr&gt;<a name="line.50"></a>
<FONT color="green">051</FONT>         *     &lt;td valign=top&gt;<a name="line.51"></a>
<FONT color="green">052</FONT>         *       &amp;nbsp;<a name="line.52"></a>
<FONT color="green">053</FONT>         *     &lt;/td&gt;<a name="line.53"></a>
<FONT color="green">054</FONT>         *     &lt;td valign=top&gt;<a name="line.54"></a>
<FONT color="green">055</FONT>         *       lex.front() == expectedTokenType<a name="line.55"></a>
<FONT color="green">056</FONT>         *     &lt;/td&gt;<a name="line.56"></a>
<FONT color="green">057</FONT>         *     &lt;td valign=top&gt;<a name="line.57"></a>
<FONT color="green">058</FONT>         *     &lt;/td&gt;<a name="line.58"></a>
<FONT color="green">059</FONT>         *   &lt;/tr&gt;<a name="line.59"></a>
<FONT color="green">060</FONT>         *   &lt;/tr&gt;<a name="line.60"></a>
<FONT color="green">061</FONT>         *   &lt;tr&gt;<a name="line.61"></a>
<FONT color="green">062</FONT>         *     &lt;td valign=top&gt;<a name="line.62"></a>
<FONT color="green">063</FONT>         *       &lt;b&gt;Postcondition&lt;/b&gt;:<a name="line.63"></a>
<FONT color="green">064</FONT>         *     &lt;/td&gt;<a name="line.64"></a>
<FONT color="green">065</FONT>         *     &lt;td valign=top&gt;<a name="line.65"></a>
<FONT color="green">066</FONT>         *       expectedTokenType = null &amp;rArr; result = null <a name="line.66"></a>
<FONT color="green">067</FONT>         *     &lt;/td&gt;<a name="line.67"></a>
<FONT color="green">068</FONT>         *     &lt;td valign=top&gt;<a name="line.68"></a>
<FONT color="green">069</FONT>         *       AND<a name="line.69"></a>
<FONT color="green">070</FONT>         *     &lt;/td&gt;<a name="line.70"></a>
<FONT color="green">071</FONT>         *   &lt;/tr&gt;<a name="line.71"></a>
<FONT color="green">072</FONT>         *   &lt;tr&gt;<a name="line.72"></a>
<FONT color="green">073</FONT>         *     &lt;td valign=top&gt;<a name="line.73"></a>
<FONT color="green">074</FONT>         *       &amp;nbsp;<a name="line.74"></a>
<FONT color="green">075</FONT>         *     &lt;/td&gt;<a name="line.75"></a>
<FONT color="green">076</FONT>         *     &lt;td valign=top&gt;<a name="line.76"></a>
<FONT color="green">077</FONT>         *       expectedTokenType &amp;ne; null &amp;rArr;<a name="line.77"></a>
<FONT color="green">078</FONT>         *         result = lex'.front() AND lex = lex'.popFront()<a name="line.78"></a>
<FONT color="green">079</FONT>         *     &lt;/td&gt;<a name="line.79"></a>
<FONT color="green">080</FONT>         *     &lt;td valign=top&gt;<a name="line.80"></a>
<FONT color="green">081</FONT>         *     &lt;/td&gt;<a name="line.81"></a>
<FONT color="green">082</FONT>         *   &lt;/tr&gt;<a name="line.82"></a>
<FONT color="green">083</FONT>         * &lt;/table&gt;<a name="line.83"></a>
<FONT color="green">084</FONT>         *<a name="line.84"></a>
<FONT color="green">085</FONT>         * @throws ParserException<a name="line.85"></a>
<FONT color="green">086</FONT>         *<a name="line.86"></a>
<FONT color="green">087</FONT>         * @param lex We are going to try and get the next token from lex.<a name="line.87"></a>
<FONT color="green">088</FONT>         * @param expectedTokenType The token type that lex[0] must be.<a name="line.88"></a>
<FONT color="green">089</FONT>         *<a name="line.89"></a>
<FONT color="green">090</FONT>         * @return the next token in &lt;b&gt;Lex&lt;/b&gt; if it is of the proper type.<a name="line.90"></a>
<FONT color="green">091</FONT>         * @see<a name="line.91"></a>
<FONT color="green">092</FONT>         *   &lt;a href=<a name="line.92"></a>
<FONT color="green">093</FONT>         *      "../../srchtml/project3/Node.html#checkFor"<a name="line.93"></a>
<FONT color="green">094</FONT>         *      &gt;Source Code<a name="line.94"></a>
<FONT color="green">095</FONT>         *   &lt;/a&gt;<a name="line.95"></a>
<FONT color="green">096</FONT>         */<a name="line.96"></a>
<FONT color="green">097</FONT>        public Token checkFor(Lex lex, TokenType expectedTokenType)<a name="line.97"></a>
<FONT color="green">098</FONT>            throws ParserException<a name="line.98"></a>
<FONT color="green">099</FONT>        {<a name="line.99"></a>
<FONT color="green">100</FONT>            assert lex != null;<a name="line.100"></a>
<FONT color="green">101</FONT>    <a name="line.101"></a>
<FONT color="green">102</FONT>            Token result = null;<a name="line.102"></a>
<FONT color="green">103</FONT>     <a name="line.103"></a>
<FONT color="green">104</FONT>            if(expectedTokenType == null){<a name="line.104"></a>
<FONT color="green">105</FONT>               //do nothing<a name="line.105"></a>
<FONT color="green">106</FONT>            } else if(lex.front().getTokenType() == expectedTokenType){<a name="line.106"></a>
<FONT color="green">107</FONT>                result = lex.front();<a name="line.107"></a>
<FONT color="green">108</FONT>                lex.popFront();<a name="line.108"></a>
<FONT color="green">109</FONT>            } else {<a name="line.109"></a>
<FONT color="green">110</FONT>                throw new ParserException(lex.front());<a name="line.110"></a>
<FONT color="green">111</FONT>            };<a name="line.111"></a>
<FONT color="green">112</FONT>            return result;<a name="line.112"></a>
<FONT color="green">113</FONT>        }<a name="line.113"></a>
<FONT color="green">114</FONT>    }<a name="line.114"></a>




























































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